1. Field of the Invention
The present invention relates to measurement of the properties of materials, and particularly to a system and method for measuring the porosity of concrete and similar aggregate materials. More particularly, the system and method are used for measuring porosity of high strength and high performance concrete.
2. Description of the Related Art
Water absorption of aggregates is a parameter that is routinely analyzed in the design and construction of roads and structures. The ability to accurately measure water absorption of materials in a repeatable manner and in a relatively short time frame is of relative importance for engineers and practitioners interested in assessing the suitability of bulk materials and material mixtures in their projects. For example, water absorption and porosity values can yield important information about the hydraulic properties of soils and aggregates.
In the asphalt mix design industry, the absorption of aggregates in a particular design, which can include both fine and coarse aggregates, is an important assessment of the quality and suitability of the asphalt design to a particular application. The design selection of materials can be a mixture or composition of aggregates of various sizes in an assortment of different materials that can be varied to yield the desired functional characteristics or standards.
Conventional methods for measuring porosity in fine aggregates, such as concrete, typically require that a material sample of the aggregate be first oven-dried to a constant weight. The material sample is then immersed in water for a 24-hour saturation period. The sample is then spread on a flat surface and exposed to a gently moving stream of warm air until a saturated surface-dry condition is reached. To assess when the saturated surface-dry condition has been reached, the material sample is positioned into an inverted cone and lightly compacted. The cone is removed, and if the material “slumps”, the material sample is considered to be in a saturated surface-dry condition. The amount of “slump” that is measured when the saturated surface-dry condition has been reached can vary from test-to-test and is operator-dependent.
Some laboratories or agencies define this condition as one in which the slump corresponds to the diameter of a dime from the top of the cone. The amount of slump can be adjusted by repetitive drying of the aggregates until the desired slump is achieved. However, if the aggregate sample is over-dried during the test procedure, the sample must be re-saturated and the drying process repeated.
After the material sample has reached the saturated dry-surface condition, a portion of the material sample is placed in a flask, which is then filled with water to a calibrated level and weighed. The fine aggregate material sample is removed from the flask and oven-dried to a constant weight. The specific gravity (apparent and bulk) and absorption are then calculated based on the three measured weights (the weight of the oven-dried sample, the weight of the flask filled with water, and the weight of the flask with the material and specimen and water to a calibration mark).
Angular fine aggregates with high absorption characteristics and/or rough surface textures do not typically slump readily. Therefore, determining the saturated surface dry (SSD) weight for samples that include these types of materials can be difficult with the cone method described above. Unfortunately, incorrect determination of this parameter in the testing process can have undesirable effects on the performance or service life of the asphalt pavement or other structure made using incorrectly analyzed materials.
In the concrete industry, the same cone test is typically used to determine the SSD condition in fine materials to determine the proper amount of water to add to the concrete mixture. Proportioning the concrete mixture with an incorrect amount of water can negatively affect the strength and durability of the concrete structures. Other commonly used methods for measuring absorption and porosity in concrete, mortar and the like include helium pycnometry, mercury intrusion porosimetry and other saturation methods, which all suffer from the repeatability problems discussed above.
For conventional concrete samples (e.g., “normal” strength concrete), conventional testing methods, such as the RILEM CPC 11.3: 1984 method (a vacuum saturation process), may be used, due to its relatively full saturation of the test samples. However, for high strength and high performance concrete samples, the RILEM CPC 11.3: 1984 method does not provide accurate measurement results because high strength and high performance concretes typically have tighter and fewer pores, with respect to conventional concrete. Thus, the RILEM CPC 11.3: 1984 method does not achieve full saturation for high strength and high performance concrete samples. Full saturation is required for accurate measurements of concrete porosity. Thus, a system and method for measuring porosity of concrete solving the aforementioned problems is desired.